THS4501CD datasheet(21/37 Pages) TI

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THS4500

THS4501

SLOS350D − APRIL 2002 − REVISED JANUARY 2004

www.ti.com

APPLICATION INFORMATION

FULLY DIFFERENTIAL AMPLIFIERS

Differential signaling offers a number of performance

advantages in high-speed analog signal processing

systems, including immunity to external common-mode

noise, suppression of even-order nonlinearities, and

increased dynamic range. Fully differential amplifiers not

only serve as the primary means of providing gain to a

differential signal chain, but also provide a monolithic

solution

for

converting

single-ended

signals

into

differential

signals

for

easier, higher performance

processing. The THS4500 family of amplifiers contains

products in Texas Instruments’ expanding line of

high-performance fully differential amplifiers. Information

on fully differential amplifier fundamentals, as well as

implementation specific information, is presented in the

applications section of this data sheet to provide a better

understanding of the operation of the THS4500 family of

devices, and to simplify the design process for designs

using these amplifiers.

Applications Section

D Fully Differential Amplifier Terminal Functions

D Input Common-Mode Voltage Range and the

THS4500 Family

D Choosing the Proper Value for the Feedback and

Gain Resistors

D Application Circuits Using Fully Differential

Amplifiers

D Key Design Considerations for Interfacing to an

Analog-to-Digital Converter

D Setting the Output Common-Mode Voltage With the

VOCM Input

D Saving Power with Power-Down Functionality

D Linearity: Definitions, Terminology, Circuit

Techniques, and Design Tradeoffs

D An Abbreviated Analysis of Noise in Fully

Differential Amplifiers

D Printed-Circuit Board Layout Techniques for Optimal

Performance

D Power Dissipation and Thermal Considerations

D Power Supply Decoupling Techniques and

Recommendations

D Evaluation Fixtures, Spice Models, and Applications

Support

D Additional Reference Material

FULLY DIFFERENTIAL AMPLIFIER

TERMINAL FUNCTIONS

Fully differential amplifiers are typically packaged in

eight-pin packages as shown in the diagram. The device

pins include two inputs (VIN+, VIN−), two outputs (VOUT−,

VOUT+), two power supplies (VS+, VS−), an output

common-mode control pin (VOCM), and an optional

power-down pin (PD).

IN− 1

OCM

S+

OUT+

IN+

S−

OUT−

Fully Differential Amplifier Pin Diagram

A standard configuration for the device is shown in the

figure. The functionality of a fully differential amplifier can

be imagined as two inverting amplifiers that share a

common noninverting terminal (though the voltage is not

necessarily fixed). For more information on the basic

theory of operation for fully differential amplifiers, refer to

the Texas Instruments application note titled Fully

Differential Amplifiers, literature number SLOA054.

INPUT COMMON-MODE VOLTAGE RANGE

AND THE THS4500 FAMILY

The key difference between the THS4500/1 and the

THS4502/3 is the input common-mode range for the two

devices. The THS4502 and THS4503 have an input

common-mode range that is centered around midrail, and

the THS4500 and THS4501 have an input common-mode

range that is shifted to include the negative power supply

rail. Selection of one or the other is determined by the

nature of the application. Specifically, the THS4500 and

THS4501

are

designed

for

use

single-supply

applications where the input signal is ground-referenced,

as depicted in Figure 97. The THS4502 and THS4503 are

designed for

use

in single-supply or split-supply

applications where the input signal is centered between

the power supply voltages, as depicted in Figure 98.

Figure 97

VOCM

+VS

Rg1

Rg2

Rf1

Rf2

−

Application Circuit for the THS4500 and THS4501,

Featuring Single-Supply Operation With a

Ground-Referenced Input Signal

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